package test_socket;

import java.io.IOException;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.DatagramChannel;
import java.util.Date;

public class MainClass {

  public static void main(String[] args) throws IOException {

    DatagramChannel channel = DatagramChannel.open();
    SocketAddress address = new InetSocketAddress(0);
    DatagramSocket socket = channel.socket();
    socket.bind(address);

    SocketAddress server = new InetSocketAddress("time-a.nist.gov", 37);
    channel.connect(server);

    ByteBuffer buffer = ByteBuffer.allocate(8);
    buffer.order(ByteOrder.BIG_ENDIAN);
    // send a byte of data to the server
    buffer.put((byte) 0);
    buffer.flip();
    channel.write(buffer);

    // get the buffer ready to receive data
    buffer.clear();
    // fill the first four bytes with zeros
    buffer.putInt(0);
    channel.read(buffer);
    buffer.flip();

    // convert seconds since 1900 to a java.util.Date
    long secondsSince1900 = buffer.getLong();
    long differenceBetweenEpochs = 2208988800L;
    long secondsSince1970 = secondsSince1900 - differenceBetweenEpochs;
    long msSince1970 = secondsSince1970 * 1000;
    Date time = new Date(msSince1970);

    System.out.println(time);
  }
}